Excitatory amino acids (EAA's) are involved in the transmission or processing of sensory information in the spinal cord. Many of the neuronal elements, however, that use or are affected by EAA's presently are unknown. This project will examine excitatory amino acid circuitry in areas of the spinal dorsal horn related to the transmission and processing of sensory messages. The specific goal of this proposal is to determine the anatomical distribution and arrangement of spinal cord components involved in excitatory amino acid synaptic transmission. The distribution of EAA's or enzymes involved in the metabolism of EAA's will be examined using immunohistochemical techniques in the dorsal root ganglia and spinal cord of rats and cats at the light and electron microscopic level. Glutamate, aspartate, glutaminase, aspartate amino transferase, glutamine synthetase, glutamate dehydrogenase, and N-acetylaspartylglutamate will be studied. The EAA receptor subtype, NMDA, will be studied with a recently described antagonist, CPP. The binding characteristics of (3H)CPP will be determined on tissue sections and autoradiography (AR) will be used to study the anatomical distribution of (3H)CPP binding. Dorsal rhizotomy and neonatal capsaicin treatment will be used with (3H)CPP-AR to study changes in distribution or number of binding sites in response to a loss of primary afferents. Rhizotomy and capsaicin will used with immunostaining for EAA's or EAA enzymes to study putative EAA-containing primary afferents. The relationship of EAA's and EAA enzymes to primary afferent terminals will be examined with electron microscopy by combining immunohistochemistry with primary afferent labelling. Neurons with supraspinal projections will be labelled with retrograde tracers and immunohistochemistry will be used to determine the EAA content of these cells and the distribution of EAA fibers contacting these cells. The neurochemical content of fibers contacting EAA- containing spinal neurons will be studied with double labelling techniques. The results from experiments outlined in this proposal will reveal important information concerning the synaptic circuitry of excitatory amino acids in sensory pathways.